Activation of the vascular endothelium in the retina was studied in the model of experimental autoimmune uveitis in the rat (retinal S antigen model). Immunohistochemical techniques were used to characterize the expression of fibronectin, Ia and Ie antigens (class II antigens). Results showed that fibronectin appears several days prior to the cellular infiltrate, Ie antigen appears 2 days prior to infiltration, and Ia appears at the time of cellular infiltration. This indicates that the vascular endothelium, which comprises retinal inflammation to occur, is activated prior to the cellular infiltration, any may therefore play a role in the local recruitment and development of uveitis in this model. Class II antigens are also expessed on other cell types during this ocular inflammation. This includes cells of the cornea, sclera, and retinal pigment epithelium. In vitro induction of class II antigens was demonstrated on cells of the cornea (human, rat), conjunctiva (rat), and sclera (rat) by the addition of gamma interferon-containing supernatants. Preliminary results show that Ia-positive corneal cells in culture may be inhibitory in antigen-presentation to T cells. Studies on retinal vascular endothelium in culture are currently being pursued.